Does the extending configuration feature work?

Opening this as a question as I’m not yet sure whether it’s a bug or a user error 😄

The docs on extending configuration state:

Configurations can inherit from other modules using the extends keyword

However, I’ve been unable to get this to work and I haven’t been able to find any Mocha-specific examples leveraging extends. I’ve tried using extends both with a relative path to a json file, as well as with a module as referenced in the yargs docs linked from the Mocha docs, and I also tried the various Mocha config file formats (js, yaml, json, etc.) to define the Mocha config with the extends keyword, all to no avail.

I created a really simple repo here that reproduces this behavior:

ui should be set to tdd via the extends reference in the .mocharc.yml file, but running an npm test results in a reference error ReferenceError: suite is not defined leading me to believe that extends is not working since the ui is still set to the default bdd

Any help would be greatly appreciated!

[juergba]

@calebcartwright yes, that would have been the test I had in mind. Thanks for your investigations.

I did some tests and my conclusion is: in some edge cases it works, but in general it does not work. So yes, a bug.

• extends is a Yargs feature, which in Mocha runs too late, when all CLI plus config options have been read and default values have been set. Furthermore it runs outside of the public loadOptions() function.
• extends should run earlier in Yargs-parser, which has a similar feature config. there could be a conflict: Mocha config <==> yargs-parser config
• which priority between extend object and configObjects (and default values)?

[mf-pherlihy]

https://github.com/mochajs/mocha/pull/4407